1. Field of the Invention
This invention relates to a mine roof support system and more particularly to a lightweight automated temporary roof support system carried by mobile mining equipment.
2. Description of the Prior Art
Ever since mining began, engineers have sought better methods of providing mine roof support. The dangers from cave-ins and even smaller amounts of rock breaking off the roof have always made this occupation one of the most hazardous. As a result, stricter standards are continually being enacted and enforced for the protection of mine workers.
Originally, wooden timbers cut to length and set upright provided the only roof support. While this system was considerably better than no support at all, it had several disadvantages. Since the timbers had to rest on the floor of the mine, they were often in the way, particularly when large machinery replaced manpower in the mines. Workers have often been caught and crushed between moving machines and the timbers.
A better method of support is currently used by suspending the roof from the more solid rock strata above it using roof bolts. Essentially, a hole is drilled into the roof and a long bolt inserted in it. A plate is placed over the end of the bolt and against the roof. As the bolt is tightened, an expansion nut at the upper end of the bolt expands, anchoring the bolt into the rock at that level and supporting the roof by the roof plate. Mobile roof bolting machines are now common in mines and provide a safe roof support system for the miners.
Unfortunately, the roof bolter operator, in his attempts to make the mine safe for others, now becomes the person most susceptible to injury. Rock falling from the roof either before the support can be installed or from the bolt installation process itself, can injure or kill the unsuspecting operator. In particular, statistics have shown that most of the accidents occur while positioning temporary supports in the form of timbers or metal jacks before installing the roof bolts. In response to this, states are beginning to enact regulations requiring bolting machines to be equipped with an automated temporary roof support (ATRS) which can position a temporary support from an area that already has permanent support. Several types of systems have been designed to implement this kind of protection.
U.S. Pat. No. 3,892,100 shows a self-propelled roof bolter having the capability of moving an extendable temporary roof support into place before the roof bolting operation. The temporary support is self-standing and carried into place by an arm having a hook at the front end. Once it is placed where desired, the support is hydraulically extended to the height of the roof and left there while the bolting operation progresses. After the roof is bolted there, the temporary support is moved to the next bolting location.
U.S. Pat. No. 4,252,475 shows another roof bolter machine having an ATRS system. The support is mounted on a boom on the front of a roof bolter. The support is pivotable by means of a hydraulic device in order to make movement of the machine easier. The boom is movable by means of another hydraulic device.
These devices and other forms of ATRS systems give additional protection to the operator of the roof bolter, but sometimes present additional problems. Devices which are detachable from the roof bolter can be cumbersome and may create a hazard in that they may slip from their position and fall. Other devices may require large amounts of space and power and also be expensive. Many otherwise usable devices have been designed into a bolter or other machine in such a way that it is not available for an easy retrofit onto existing machines.
Additional problems are involved where coal seams have low ceilings. Most equipment designed for a higher mine simply will not fit. Unfortunately, in some areas, these low seams provide the highest quality coal which is especially in demand for meeting pollution standards. It is not possible to merely size down larger machines since the individual components are weakened by the reduction in size while the stresses from the roof remain constant regardless of its height. Also, devices designed for higher seams may interfere with the working space and visibility in the tighter confines of a low seam. Accordingly, the use of such devices in low seams present many problems.